This application claims the priority benefit of Japanese Patent Application No. 10-356513, filed Dec. 15, 1998, the entire subject matter of which is incorporated herein of reference.
1. Field of the Invention
The invention relates to an attenuated phase-shift mask which is used in a lithographic process used in manufacturing a semiconductor device, and also to a method of manufacturing the device.
2. Description of the Related Art
With an increase in the level of integration of semiconductor integrated circuits, there have been rapid advances in minimizing micropatterns used for circuitry. To improve the resolution, various technologies have been applied. For example, a short wavelength or a projection lens having a high numerical aperture is used in lethographic processes. Specifically, a projection lens having high numerical apertures is effective to form a pattern having a width, which is less than the exposure wavelength. However, a high numerical aperture has resulted in an insufficient depth of focus (DOF). So, recently, a resolution enhancement technique has been proposed, in which a pattern is formed on a phase-shift mask using a phase. A variety of types of phase-shift mask has been proposed to date, including an attenuated phase-shift mask for use in production of semiconductor integrated circuits. Specifically, the attenuated phase-shift mask is proposed because of its simple construction.
The attenuated phase-shift mask includes a pattern which is formed of chromium (Cr) and a pattern called as a shifter which is formed of MoSi. A light waveform is modulated by the shifter so that the phase of the light is shifted by 180 degrees according to the following formula:
d=xcex/2(nxe2x88x921)
Where d is the thickness of the shifter, xcex is the wavelength, and n is the refractive index of the shifter.
In such an attenuated phase-shift mask, the MoSi pattern passes a few to ten-odd percent of the light whose phase is inverted from the light which passes through an area of the mask other than the pattern.
The technique is expected to improve the resoulution and the DOF by forming rectangular hole patterns whose length of the longer side is half as great as the resolution limit of the resist material, which is formed on the semiconductor substrate, in the patterns of the attenuated phase-shift mask. Futhermore, The technique is expected to improve the resolution and the DOF by forming a repeated line pattern in the patterns of the attenuated phase-shift mask when a modified illumination, such as an annular illumination, is used.
To fabricate the attenuated phase-shift mask, first, the phase shifter is formed as a layer of MoSi on a mask substrate, and then the Cr layer is formed on the MoSi layer. A first resist layer is formed on the Cr layer, and then parts of the Cr layer and the MoSi layer are removed to make a first hole in the MoSi layer by the lithographic process. After that, a second resist film is formed on the entire surface of the mask, a part of the Cr layer which surrounds the hole is removed to make a second hole in the Cr layer by an etching process. The rectangular holes having the first and second opening, whose length of the longer side is half as great as the resolution limit of the resist material formed on the semiconductor substrate, are completed.
However, if a large number of patterns of holes are formed in a large Cr pattern, the amount of CAD data requesting to form the attenuated phase-shift mask also becomes large. Further, the process for manufacturing such an attenuated phase-shift mask is complicated because, as described above, patterns should be formed twice. Also, in addition to the CAD data for patterning the Cr layer, other CAD data is required for forming the holes in the Cr pattern.
On the other hand, when the attenuated phase-shift mask having a repeated line pattern is used with an annular illumination, no problem is found when a resist pattern on the semiconductor device has a width, which is close to the resolution limit of a resist material formed on the Si substrate. However, when some patterns having a width twice as great as the resolution limit are transferred to the resist layer from the Cr mask, a bad resist profile is liable to be formed at the edge of the resist pattern. Furthermore, the thickness of the resist pattern sometimes becomes thinner at the pattern edge.
Therefore, both methods described above are not satisfied when the large resist pattern is formed.
An objective of the invention is to provide an attenuated phase-shift mask including a mask pattern which has a light shield characteristic.
Another objective of the invention is to provide an attenuated phase-shift mask including a mask pattern which causes a fine resist pattern profile to form and causes the resist pattern to have uniform thickness.
Yet another objective of the invention is to provide an attenuated phase-shift mask having a mask pattern that is formed by a small amount of CAD.
To achieve these objectives, in an attenuated phase-shift mask including a mask substrate and a rectangular pattern having a side (L) formed on the substrate, which is defined within a large pattern which is transferred on a resist material formed on a semiconductor substrate, the rectangular pattern includes a plurality of first opaque patterns, each having a width (ML) equal to 1 to 1xc2xd times the resolution limit of the resist material at least one transparent opening pattern, having a width (MS) less than half the resolution limit, and wherein the number (X) of the opaque patterns and transparent opening patterns is determined by the following equations:
X=2P+1,
where
P=ROUND UP ((Lxe2x88x92ML)/(ML+MS)),
where the term xe2x80x9cROUND UPxe2x80x9d defines that P takes a value of the next highest integer value if (Lxe2x88x92ML) divided by (ML+MS) is not an integer.
Furthermore, to achieve these objectives, in an attenuated phase-shift mask including a mask substrate and a rectangular pattern having a side (L) formed on the substrate, which is defined within a large pattern which is transferred on a resist material formed on a semiconductor substrate, the rectangular pattern includes a frame shaped opaque pattern having a width (ML1) equal to 1 to 1xc2xd times the resolution limit of the resist material, a rectangular area spaced from the frame shaped opaque pattern having a width (MS2) less than half the resolution limit, the area having a plurality of first opaque patterns, each having a width (ML2) equal to 1 to 1xc2xd times the resolution limit and a transparent opening pattern having a width (MS2) less than half the resolution limit, and wherein the number (X) of the opaque patterns and transparent opening patterns is determined by the following equations:
X=2P+1,
where
P=ROUND UP ((Lxe2x88x922(ML1+MS1)-ML1)/(ML1+MS2)),
where the term xe2x80x9cROUND UPxe2x80x9d defines that P takes a value of the next highest integer value if (Lxe2x88x922(ML1+MS)xe2x88x92ML1) divided by (ML1+MS2) is not an integer.
Further, to achieve these objectives, in an attenuated phase-shift mask including a mask substrate and a rectangular pattern formed on the substrate, which is defined within a large pattern which is transferred on a resist material formed on a semiconductor substrate, the rectangular pattern includes a frame shaped opaque pattern having a width equal to 1 to 1xc2xd times the resolution limit of the resist material, a frame shaped transparent opening pattern having a width less than half the resolution limit, the frame shaped transparent opening pattern being surrounded by the frame shaped opaque pattern, and an rectangular opaque pattern which is surrounded by the frame shaped transparent opening pattern.
Also, to achieve these objectives, in an attenuated phase-shift mask including a mask substrate and a rectangular pattern formed on the substrate, which is defined within a large pattern which is transferred on a resist material formed on a semiconductor substrate, the rectangular pattern includes four rectangular transparent opening patterns, each having a width less than the resolution limit of the resist material, which is elongated along one of each side of the rectangular pattern, and is spaced from each side of the rectangular pattern by a distance, which is more than the resolution limit of the resist material.